You may have heard that diabetes causes eye problems and may lead to blindness. People with diabetes do have a higher risk of blindness than people without diabetes, but most diabetics have nothing more than minor eye disorders. Regular examination can keep minor problems minor, and if major problems do develop, there are often treatments that work quite well if begun promptly.
To understand what happens in eye disorders, it helps to first understand how the eye works. The eye is a ball covered with a tough outer membrane. The covering in front is clear and curved. This curved area is the cornea, which focuses light while protecting the eye.
After light passes through the cornea, it travels through a space called the anterior chamber (which is filled with a protective fluid called the aqueous humor), through the pupil (which is a hole in the iris, the colored part of the eye), and then through a lens that performs more focusing. Finally, light passes through another fluid-filled chamber in the center of the eye (the vitreous) and strikes the back of the eye, the retina.
Like the film in a camera, the retina records the images focused on it. But unlike film, the retina also converts those images into electrical signals, which the brain receives and decodes. In effect, we “see” in our brain, using information sent by our eyes.
One part of the retina is specialized for seeing fine detail. This tiny area of extra-sharp vision is called the macula.
Blood vessels in and behind the retina nourish the macula. The smallest of these blood vessels are the capillaries.
People with diabetes are 40% more likely to suffer from glaucoma than people without diabetes. The longer someone has had diabetes, the more common glaucoma. Risk also increases with age.
Glaucoma occurs when pressure builds up in the eye. In most cases, the elevated pressure is caused by an imbalance in the production and drainage of the aqueous humor inside the eye. The pressure pinches the blood vessels that carry blood to the retina and optic nerve. Vision is gradually lost because the retina and nerve are damaged.
There are several treatments for glaucoma. Some use drugs to reduce pressure in the eye, while others involve surgery.
Many people without diabetes develop cataracts, but people with diabetes are 60% more likely to develop this eye condition. People with diabetes also tend to get cataracts at a younger age and have them progress faster. With cataracts, the eye’s clear lens clouds, blocking the entrance of light and leading to decreased vision.
To help deal with mild cataracts, new glasses may be of benefit. Anti-glare coatings or sunglasses may be recommended. For cataracts that interfere greatly with vision, cataract surgery (removal of the cloudy lens) may be more effective.
Diabetic retinopathy is a general term for all disorders of the retina caused by diabetes. There are two major types of retinopathy: nonproliferative and proliferative.
Nonproliferative retinopathy is the most common form of retinopathy. In nonproliferative retinopathy, capillaries in the back of the eye balloon and form pouches. Nonproliferative retinopathy can move through three stages (mild, moderate, and severe), as more and more blood vessels become blocked. Although retinopathy does not usually cause vision loss at this stage, the capillary walls may lose their ability to control the passage of substances between the blood and the retina. Fluid can leak into the part of the eye where focusing occurs, the macula. When the macula swells with fluid, a condition called macular edema occurs and vision can decrease significantly. Although nonproliferative retinopathy usually does not require treatment, macular edema must be treated. Fortunately, treatment is usually effective at stopping, and often even reversing, vision loss.
In some people, retinopathy progresses to a more serious form called proliferative retinopathy. In this form, the blood vessels are so damaged, they close off. In response, new blood vessels start growing in and around the retina. These new vessels are weak and can leak blood, blocking vision, which is a condition called vitreous hemorrhage. The new blood vessels can also cause scar tissue to grow. After the scar tissue shrinks, it can distort the retina or pull it out of place—causing what is called “retinal detachment.”
The retina can be severely damaged before there are any noticeable changes to the vision. Most people with nonproliferative retinopathy have no symptoms. Even with proliferative retinopathy, the more dangerous form, people sometimes have no symptoms until it is too late to be treated. For this reason, all diabetics should have their eyes examined at least yearly.
Several factors influence whether you get retinopathy. They include blood sugar control, blood pressure levels, duration of diabetes, and genetics. The longer you have had diabetes, the more likely you are to have retinopathy. Almost everyone with type 1 diabetes, and many with type 2, will eventually have nonproliferative retinopathy. Serious proliferative retinopathy is far less common.
People who keep their blood sugar levels closer to normal are less likely to develop serious diabetic changes in the eye, as well as in the rest of the body.
Huge strides have been made in the treatment of diabetic retinopathy. Treatments such as administration of medications, scatter photocoagulation, focal photocoagulation, and vitrectomy prevent blindness in most people. The sooner retinopathy is diagnosed, the more likely these treatments will be successful. The best results occur when sight is still normal. The latest advances in retinal treatment have involved injectable medications. Success can often be obtained without the need for either laser or surgery.
In photocoagulation, the eye care professional makes tiny spots on the retina with a special laser. These spots seal the blood vessels and stop them from growing and leaking.
In scatter photocoagulation (also called panretinal photocoagulation), the eye care professional makes hundreds of spots in a polka-dot pattern on two or more occasions. Scatter photocoagulation reduces the risk of blindness from vitreous hemorrhage or detachment of the retina; this is most effective before bleeding or detachment has advanced too far. Scatter photocoagulation is also used for some kinds of glaucoma.
Side effects of scatter photocoagulation are usually minor. They include several days of blurred vision after each treatment and possible loss of side (peripheral) vision.
In focal photocoagulation, the eye care professional aims the laser precisely at leaking blood vessels in the macula. This procedure assists the body in reabsorbing the fluid, which can aid in visual restoration.
When the retina has already detached, or a lot of blood has leaked into the eye, photocoagulation is no longer useful. The next option is vitrectomy, which is surgery to remove scar tissue and cloudy fluid from inside the eye. The earlier the operation occurs, the more likely it is to be successful.